Resistance unit and element thereof



4, 1953 A. c. DYER 2,647,978

RESISTANCE UNIT AND ELEMENT THEREOF Filed Aug. 11, 1951 5 Sheets-Sheet 1IN V EN TOR.

Aug. 4, 1953 A. c. DYER RESISTANCE UNIT AND ELEMENT THEREOF Filed Aug.11, 1951 5 Sheets-Sheet 2 INVENTOR.

ALVIN G. DYER' Aug. 4, 1953 A. c. DYER RESISTANCE UNIT AND ELEMENTTHEREOF 5 Sheets-Sheet 5 Filed Aug. 11 1951 INVENTOR.

5 v, R g E? p m 6% a M L A B A 1953 A. c. DYER, 2,647,978

RESISTANCE UNIT AND ELEMENT THEREOF Filed Aug. 11, 1951 5 Sheets-Sheet 4IN VEN TOR.

Aug. 1953 A. c. DYER 2,647,978

RESISTANCE UNIT AND ELEMENT THEREOF Filed Aug. 11, 1951 5 Sheets-Sheet 5laz mm m 'w Patented Aug. 4, 1953 RESISTANCE UNIT AND ELEMENT THEREOFAlvin C. Dyer, Shaker Heights, Ohio, assignor to The Electric Controller& Manufacturing Company, Cleveland, Ohio, a corporation of OhioApplication August 11, 1951, Serial No. 241,408

This invention relates to electric resistance elements and electricresistance units containing the same, and more particularly to compositeresistance elements formed by attaching a pair of individual resistancegrids, preferably stamped from sheet metal, to a common supportingmember which also serves as a wiring terminal and to resistance unitswhich comprise an assemblage of such composite resistance elements andwhich are suitable for various purposes such as, for example, thecontrol of electric motors of the smaller integral horsepower sizes.

A general object of this invention is to provide a resistance unit orresistor possessing the advantages of the resistor disclosed and claimedin David C. Wright Patent No. 2,378,056 issued on June 12, 1945, butcapable of having a wider range of resistance per unit volume,particularly a greater resistance per unit volume, and of having alarger number of intermediate taps.

In the resistor of the Wright patent, lug portions at opposite ends of asheet metal resistance element shaped in the form of a grid are oiTs-etin opposite directions from the plane of the intermediate portion of thegrid and lie in respec- 17 Claims. (Cl. 201-459) tive planes which arespaced from but parallel to v the plane of the intermediate portion.When a plurality of the grids of the patent are properly assembled infiatwise spaced relation on a supporting means to form a resistor, thelug portions at a given end of a pair of adjacent grids extend away fromeach other and the lug portions at the other end of the same adjacentgrids extend toward and engage each other. The lug portions inengagement with each other are spot welded together after the resistoris assembled.

Resistors such as disclosed in the Wright patent and using grids stampedfrom a chromiumaluminum-steel alloy of high specific resistance arecurrently being manufactured with a minimum continuous rating of 32amperes at a temperature rise of 375 degrees centigrade. The resistorsof this rating with forty-eight grids have a resistance of approximatelyseven ohms.

A more specific object of this invention is to provide a resistor of thesame or similar outline dimensions which has a resistance considerablyin excess of seven ohms and which is capable of having a larger numberof intermediate taps than the resistor of the Wright patent, thusenabling more precise selection of increments of the total resistance ofthe resistor for utilization in an external circuit.

Since suitable metals or alloys of higher specific resistance than thealloy described above are not available, the resistance of a resistorbuilt in accordance with the disclosure of the Wright patent can beincreased only by decreasing the crosssectional area of the current paththrough the grids, using more grids, making the current path of eachgrid longer, or by a combination of any two or all three of theseexpedients. To provide the desired higher resistance by reducing thecross-sectional area of the current path through grids proportioned andsupported like those of the Wright patent, either by using thinner metalor narrowing the width of the grid bars, or both, is not a satisfactorysolution of the problem beyond a limited range because the grids becometoo flexible and have to be supported at so many intermediate locationsthat the cost of the resistor is materially increased and its heatdissipating ability is seriously impaired. Increasing the length of thegrids or using more grids in flatwise spaced relation likewsie are notadequate solutions of the problem because the ratio of resistance tounit volume is either lessened or not materially increased and the shapeand outline dimensions of the resistor deviate too much from standardpractice. Furthermore, none of these expedients, or any combination ofthem, results in a resistor which can be provided conveniently with thedesired large number of intermediate taps. For these and other reasonsit is not practicable economically to manufacture resistors such asdisclosed in the Wright patent which have the desired higher resistanceor the'greater number of taps.

Accordingly, another object of the present invention is to provide animprovement of the resistor of the Wright patent capable of beingmanufactured economically with a much larger resistance per unit volumeand without deviation from standard outline dimensions for suchresistors.

A further object is to obtain the increased resistance to volume ratioby the provision of a novel composite resistance element formed by spotwelding a pair of identical sheet metal grids to a common combinedterminal and supporting member. The composite resistance element inaccordance with this invention has a longer current path for a givenarea than prior resistance elements, and the individual grids thereofare so proportioned and arranged in cooperation with novel combinedterminal and supporting members that they can be made of relatively thinmetal and have relatively narrow grid bars and still be convenientlysupported for operation at elevated temperatures The cooperativerelation between the individual grids and the combined terminal andsupporting members is such that taps to which lead-in conductors can besecured are provided at opposite ends of each of the individualidentical grids thereby to provide the desired large number ofintermediate taps. The principal advantages of the off-set end portionsof the grids vof the .prior resistor are retained in the improvedresistor.

Additional objects are to provide an improved composite resistanceelement, to provide a composite resistance element :comprising a :pair:of substantially coplanar identical sheet metal resistance elementssecured to and extending in the same direction from a common :combinedterminal and supporting member, to provide an improved electric resistorcomprising .a plurality of composite resistance elements arrangedinflatwise spaced relation and having a relatively'large number ofintermediate taps, to provide an improved resistor comprising anassemblage of fiatwise spaced resistance elements than can beeconomically manufactured with a relatively large resistance per unitvolume, to provide a resistor comprising a spot-welded assemblage ofcomposite resistance elements of improved design, and to provide anelectric resistor in which a plurality of complementary compositeresistance elements are supported in flatwise spaced relation with anoffset portion of each of the elements extending toward and engaging aportion of an adjacent element at an area accessible for spot-weldingtherebetween.

An individual resistance element of the composite resistance element ofthis invention preferably is stamped from resistive sheet metal in theform of a relatively long and narrow substantially uniplanular gridhaving a plurality of relatively narrow transverse grid bars ofsubstantially the same width. The bars at opposite ends of the gridconstitute respective lug portions one of which is in the plane of thegrid and the other of which is offset so that its terminal portion isspaced from and parallel to the plane of the remainder of the grid.Apair of the individual grids are assembled into a composite resistanceelement by spot-welding the respective end bars thereof that are notoffset to respective tongue portions of a common combined terminal andsupporting member. sembled into acomposite resistance element, the pairof individual grids are arranged in edgewise spaced relation in a commonplane with their respective longitudinal axes parallel to each other andwith the respective offset end bars of the two individual grids offsetin opposite directions from the plane of the remainder of the compositeresistance element. The composite resistance element is completed byspot-welding another of the combined terminal and supporting members toone of the two offset end bars.

A resistor in accordance with this invention comprises an assemblage ofsuch composite resistance elements held in fiatwise spaced relation by asupporting means with those of the respective terminal members which arespot welded to the ofi-set end bars extending toward and in engagementwith the respective oppositely off-set end bars of adjacent compositeresistance elements which do not have terminal members welded to them.After the resistor is assembled on the supportingmeans, spot Welds aremade between these terminal members and these oppositely oif-set endbars engaged thereby. Alternate ones of the composite resistance ele-When asments have terminal members of slightly different configurationfrom each other so that extending portions of adjacent terminal membersare spaced apart to provide adequate electrical clearance and tofacilitate accessibility and the connection of lead-in conductorsthereto.

Other objects and advantages of this invention will become apparent fromthe following specification wherein reference is made to theaccompanying drawings, in which Fig. l is an exploded perspective viewshowing how a pair of the composite resistance elements of thisinvention are complementary to each other when arranged side by side ona pair of supporting bolts,

Fig. 2 is a sectional view taken generally along :thedine 2-2-of Fig, 3,

Fig. 3 is a front elevation of a resistance unit, embodying anassemblage of the resistance elements of Fig. l, with an intermediateportion having parts at the rear of the unit omitted, and partly insection as indicated by the line 3-3 of Fig. 4,

Fig. l is a top plan View with an intermediate portion having parts atthe bottom of the unit omitted and partly in section along the line 4-4of Fig. 2,

Figs. 5 and 6 are perspective views of the combined terminal andsupporting members of the unit of Figs. 2, 3, and 4,

Fig. '7 is a fragmentary front elevation of a modified resistance unitwith parts at the rear omitted, and

Fig. 8 is a fragmentary rear elevation of the unit of Fig. '7 with partsat the front omitted.

Since the resistance unit or resistor may be used in any turned positionas well as in the position in which shown, such positionally descriptivewords as front and rear, upper and lower, and the like as used hereinare used for convenience in describing relative positions only.

Referring principally to Figs. 1 and 2, one of a pair of complementarycomposite resistance elements in accordance with this invention,indicated by the reference numeral I0, comprises a pair of identicalindividual resistance elements H suitably fastened to a common combinedterminal and supporting member 52 as by spotwelding, and another one ofthe pair of composite resistance elements, indicated by the referencenumeral M, comprises a pair of the individual resistance elements Hsimilarly fastened to a common combined terminal and supporting memberl5.

Each of the individual resistance elements I i is preferably anintegral. piece of sheet metal of suitable thermal, mechanical andelectrical characteristics, such a high resistance alloy of chromium,aluminum, and steel, and is preferably shaped in the form of anelongated grid having a plurality of parallel spaced intermediate legportions 16 transverse to its longitudinal axis and interconnectedalternately at opposite ends by connecting portions IE to form auniplanular circuitous current path between opposite end leg portions I9and 29 which are preferably parallel to the intermediate leg portions l6and which constitute supporting lugs for the individual resistanceelements or grids. An adjacent pair of the intermediate leg portions IS,preferably a pair iSa midway between the end leg portions l9 and 2B, areof reduced length and are connected by a connecting portion !8a ofcorrespondingly increased width to provide space for a circular opening2| which cooperates with an intermediate supporting means to bedescribed.

The grids I I may be formed directly from sheet metal by a stampingoperation or may be formed by edgewise bending of a long straight strip,and may be of any suitable configuration, the convolutions defined bythe leg portions I6 and connecting portions I8 being merely illustrativeof a preferred embodiment which provides a relatively long current pathWithin a relatively small area with only a small amount of metal beingwasted in the stamping operation. Preferably, the leg portions I5 arerelatively short as shown so as to impart sufficient rigidity to thegrids I I to enable them to be relatively long and to be formed ofrelatively thin sheet metal and still not vibrate excessively or warp atelevated temperatures.

The end leg 29 of each of the grids II is bent intermediate of itslength to define an angularly disposed portion 22 between an inner endportion of the leg 29 which remains in the plane of grid and an outerend portion 24 which is bent so that it lies in a plane spaced from butparallel to the plane of the remainder of the grid. The end legs aremade slightly longer than the legs I9 so that, after the bendingoperation, the end edges of the end legs I9 and 20 are substantiallyequidistant from the longitudinal center-line of the grid, Preferably,the opening 2I is on the 0pmsite side of the longitudinal center-line ofthe grid from the end edges of the legs I9 and 2B.

As shown most clearly in Figs. 1 and 5, the combined, terminal andsupporting member I2 comprises a piece of sheet metal, preferablycoldrolled steel, having a body portion 25 provide with a centrallydisposed circular opening 25. A. pair of aligned tongue portions 28 and29 extend from the top and. bottom, respectively, of the body portion 25in the plane thereof and preferably have their respective outer sideedges aligned with a side edge 30 of the body portion 25. A bracketportion 3I which extends from the top of the body portion 25 is spaced ashort distance from the tongue portion 28 and has a portion 32overhanging a side edge 33 of the body portion 25 opposite the side edge30. The bracket portion BI is bent at right angles to the plane of thebody portion 25, to the left as viewed in Fig. 5, and the overhangingportion 32 is formed to define a downwardly directed wire receivingchannel 34. Notches 35 (Fig. 1) formed in opposite side edges of theportion 32 define an intermediate portion 35 of reduced width betweenpairs of opposing shoulders 31.

As shown. most clearly in Figs. 1 and 6, the combined terminal. andsupporting member I5, which is similar to the terminal and supportingmemher I 2, has a body portion 38 provided with a centrally disposedcircular opening 39, a pair of tongue portions 44! and 4| correspondingto the tongue portions 23 and 29 of the member I2, and a bracket portion42 similar to the bracket portion 3| but bent in the opposite directionor to the right as viewed in Fig. 6. A. wire receiving channel 44 formedin an overhanging portion 45 of the bracket portion 42 opens upwardly,as viewed in Fig. 6, and notches 46 (Fig. 1) in opposite side edges ofthe overhanging portion 45 define an intermediate portion 41 of reducedwidth between pairs of opposing shoulders 48.

A pentagonal collar 49, which may be received on the overhanging portion32 of the bracket 3! of the terminal member I2 between the shoulders 37,has a set screw 58 threaded through an openinggin a relatively shortside wall 5I. The set screw 50 may be turned to engage the upper surraceof the intermediate portion 36 thereby to force a pair of side walls 52of the collar 45, which intersect at an acute angle opposite from thelower end of the set screw 50, against a leadin conductor (not shown)received in the channel 34 thereby to hold the lead-in conductor in goodelectrical contacting engagement with the terminal member I2. Similarly,a collar 48 may be received on the overhanging portion 45 of the bracket42 of the terminal member I5 between the shoulders 48 so that its setscrew 59 may be turned to engage the lower surface (Fig. 6) of theintermediate reduced portion 41 to cause a lead-in conductor (not shown)to be gripped between the acutely intersecting side walls 52 and thechannel 44.

Although the terminal members I2 and I5 are shaped to accommodate aspecific form of wire securing means, it is to be understood that theymay be arranged in other suitable ways to facilitate the attachment ofconductors thereto. For clarity of illustration, the collars 49 havebeen omitted from the resistor shown in. Figs. 1, 2, 3, and 4, it beingunderstood that they may be placed either on all or selected ones of themem bers I2 and I5 thereof.

Again referring principally to Figs. 1 and 2, each of the compositeresistance elements I 0 is assembled by overlapping the outer endportion of the end leg I9 of one of the grids II on the tongue portion28 of one of the terminal members I2 and securing it thereto as by apair of spot welds 54, and by overlapping the outer end portion of theend leg I9 of another one of the grids II on the other tongue portion 29of the same one of the members I2 and securing it thereto as by a pairof spot welds 55. When so welded to the tongue portions 28 and 29, thetwo grids I I of the resistance element I I] lie in a common plane andextend in edgewise spaced relation from the terminal member I 2 in thesame direction with their longitudinal axes parallel and, as viewed inFig. l, with the offset portion 24 of the leg 26 of the uppermost gridII offset in a direction away from the resistance element I4, and theoffset portion 24 of the leg 20 of the lowermost grid II oifset in adirection toward the resistance element I4. The offset portion 24 of theuppermost grid II overlaps the tongue portion 28 of another of theterminal members I2 and is secured thereto as by a, pair of spot Welds56. It should be noted that the terminal members I2 of each ofresistance elements II! overlap the grids II thereof on the side facingin the direction of offset of the portion 24 of the uppermost one of thegrids.

Each of the composite resistance elements I4 is assembled in a similarmanner by overlapping the outer end portion of the end leg I9 of one ofthe grids II on the tongue portion 4| of one of the terminal members I5and securing it thereto as by a pair of spot welds 53, and byoverlapping the outer end portion of the end leg I9 of another one ofthe grids II on the other tongue portion 40 of the same one of themembers I5 and securing it thereto as by a pair of spot welds 59. Whenso welded to the tongue portions 40 and M, the two grids II of theresistance element I4 are so positioned that they lie in a common planeand extend from the terminal member I5 in edgewise spaced relation inthe same direction with their longitudinal axes parallel and, as viewedin Fig. 1, with the oIT-set portion 24 of the leg 20 of the uppermostgrid II oil-set in a direction toward the resistance element I0, and theoifset portion 24 of the lowermost grid H offset in a direction awayfrom the resistance element. in. The offset portion 24 of the uppermostgrid. ll of each of the resistance elements l4 overlaps and is securedas by a pair of spot welds B to the tongue portion 4! of another of theterminal members l5. It should be noted that the terminal members E5 ofeach of the resistance elements 14, like the terminal members I2 of eachof the resistance elements l9, overlap the grids H thereof on the sidefacing in the direction of off-set of the portion 24 of the uppermostone of the grids.

The composite resistance elements If) and [4- are complementary to eachother and a complete resistor in accordance with this invention andshown in Figs. 2, 3, and 4 comprises a plurality of the elements in andI4 arranged alternately in fiatwise spaced relation along a pair ofelongated main supporting bolts 54 and 65 held in parallel spacedrelation in a manner to be described and surrounded throughout most oftheir length by respective insulating tubes 66 and 51. The resistor isassembled by slipping the openings 25 in the terminal members l2 of oneof the resistance elements 12 over the tubes 66 and 61, respectively,with the brackets 3| above the bolts 64 and 65, and then slipping theopenings 39 in the terminal members of one of the resistance elements l4over the tubes 65 and 61', respectively, with the brackets 42 below thebolts 84 and 55. Additional resistance elements to and 14 are receivedalternately in like manner on the bolts 64 and 55- until the desirednumber of elements have been assembled to form a row or stack. Since,when so assembled, the brackets 3| of the terminal members 12 are abovethe longitudinal center line of the resistor, their respective channels34 open downwardly, and since the brackets 42 of the terminal members l5are below the longitudinal center line of the resistor, their res ectivechannels 44 also open downwardly.

The uppermost grids H of the resistance elements Hi and !4 are in anupper row with their respective intermediate openings 2| in alignmentand the lowermost grids H of the resistance elements are in a lower rowwith their respective intermediate openings 2i in alignment.

The brackets 31 and 42 at the rear of the resister all extend from theirrespective terminal members i2 and 15 in the same direction or towardthe right as viewed in Figs. 3 and 4, and the brackets 3| and 42 at thefront of the resistor all extend in the same direction from theirrespective terminal members 12 and I5 or to the left as viewed in Figs.3 and 4. The brackets 34 and 42 of adjacent ones of the resistanceelements Hi and M, respectively, are thereby spaced apart from eachother both horizontally and vertically of the resistor thereby toprovide adequate electrical clearance therebetween and between lead-inconductors (not shown) connected thereto.

Since the channels 34 and 44 open downwardly, the set screws 5b of thecollars 45 when received on the brackets 3i and 42 have their respectiveheads facing upwardly, and since the brackets 3| and 42 on the same sideof the resistor extend in the same direction, clearance is provided fora screw-driver to reach the set screws 52 of the collars 49 whenreceived on the brackets 4-2 as clearly seen in Figs. 3 and 4.

Referrin particularly to Fig. 3, it will be noted that the upper offsetportions 24 of the resistance element [0 and I4 all extend in onedirection endwise of the row from the plane of their respectiveelements, and the lower ofiset portions 24 all extend in the oppositedirection. As. seen from the. front of the resistor as in Fig. 3, theupper offset portions 24 extend to the left and the lower offsetportions 24 extend to the right.

Because the elements I0 and 14 are disposed alternately in the row orstack along the bolts.

64 and 65, the terminal members l2 and I5 which depend from respectiveones of the upper offset portions 24 at the front of the resistor aredisposed alternately along the row, and their respective tongue portions29 and 40 engage the lower offset portions 24, respectively. Thus theoffset portion 24 of the lowermost grid ll of each of the resistanceelements 10 extends toward and engages in overlapping relation thetongue portion 40 of the front terminal member l5 of the next adjacentresistance element 14, and the offset portion 24 of the lowermost gridll of each of the resistance elements l4, except the one nearest an endframe 68 at the right-hand end of the row, extends toward and engages inoverlapping relation the tongue portion 29 of the front terminal memberl2 of the next adjacent resistance element In. The offset portions 24engage the respective tongue portions 29 and 40 at respective areasaccessible by the electrodes of a spot-welding machine (not shown) and,after the resistor is assembled, pairs of spot-welds (not shown) may bemade between the abutting portions 24 and tongue portions 29 and 40,respectively. The adjacent resistance elements [0 and 14 are thus heldin flatwise spaced relation at the front of the resistor and an electriccircuit is completed from element to element through spot-welds.

The main supporting bolts 64 and 65, each of which is threaded at itsopposite end portions, are received at one end in respectivehorizontally spaced openings in the end frame 68 and at the other end insimilar respective openings in an end frame 69. Preferably, the openingsin the end frames 68 and 69 are elongated horizontally, as indicated inFig. 4, so as to provide space for thermal expansion of the resistanceelements [0 and 14 carried by the bolts 64 and Each of the bolts 64 and65 is preferably insulated from the end frame 68 by an outer insulatingwasher 10 having a centrally disposed annular boss H (Fig. 4) whichextends through its associated opening in the end frame 68 into acomplementary centrally disposed cylindrical recess in an innerinsulating washer l2, and each is retained in position with respect tothe end frame 68 by inner and outer nuts 14 and 15 tightened against thewashers l2 and I0, respectively, metal washers l3 performing their usualfunction as indicated. The opposite end portion of each of the bolts 64and 65 is similarly insulated from and secured to the end frame 69.

As mentioned, the resistance elements l0 and I4 are arranged alternatelyin a row or stack along the bolts 64 and 65 with the insulating tubes 66and 61 passing through the respective openings 26 and 39 in the terminalmembers 12 and I5. The respective end portions of the resistanceelements I0 and I4 at the front of the resistor or in the region of thebolt 64 are additionally held in flatwise spaced relation by suitableheat resisting insulating washers 16 received over the insulating tube66 and interposed respectively in the spaces between adjacent ones ofthe terminal members l2 and I5 disposed along the tube 66. Similarly,the respective end portions of the elements and M at the rear of theresistor or in the region of the bolt 65 are held in fiatwise spacedrelation by additional insulating washers 16 received over theinsulating tube 61 and interposed respectively in the spaces betweenadjacent ones ofthe terminal members 2 and I5 disposed along the tube61. In other words, both at the front and rear of the resistor adjacentones of the terminal members l2 and I5 are spaced apart by engagement ofthe margin of the metal around the respective openings .26 and 39 withthe planular side faces of one of the washers 16. Additional washers 16may be placed on the insulating tubes 66 and 61, respectively, atopposite ends of the row of resistance elements, the outermost ones ofthe washers 16 at each end of the row preferably extending slightlybeyond the end of their respective tubes as shown in Fig. 4. The row ofresistance elements I0 and I4 is held together by nuts 18 threaded onthe end portions of the bolts 64 and 65, respectively, suitable lockwashers 19 and plain metal washers 89 being disposed between the nuts 18and the outermost of the insulating washers 16, respectively.

The uppermost ones of the individual grids II are supported intermediateof their respective end portions by a supporting means comprising anelongated bolt 8| passing through the aligned openings 2| in the upperrow of grids and having its opposite end portions threaded and receivedin horizontally elongated openings near the top of the respective endframes 68 and 69.

A supporting means for the intermediate portions of the lowermost onesof the individual grids comprises a similar bolt 82 passing through thealigned openings 2| in the lower row of grids and having its oppositeend portions received in respective horizontally elongated openings nearthe bottom of the respective end frames 68 and 69. Fach of the endportions of the bolts 8| and 82 is preferably secured to and insulatedfrom its associated one of the end frames 68 and 69 by a pair oftelescoping insulating washers 84 and 85, similar to the washers and 12,respectively, and outer and inner nuts 86 and 81. The upper and lowerintermediate supporting means also comprise respective groups ofinsulating washers 89 to bedescribed and received on the respectivebolts 8| and 82 thereof.

The intermediate portions of the grids I in the upper row are held infiatwise spaced relation by the group of the insulating washers 89received on the bolt 8|, and the intermediate portions of the grids IIin the lower row are held in fiatwise spaced relation by the group ofthe insulating washers 89 received on the bolt 82. As shown most clearlyin Fig. 4, each of the washers 89 has a central annular boss 90 on oneside, and, on the other side, a central cylindrical recess 9| ofslightly larger diameter than the boss 90 and slightly deeper than theheight of the boss 99. Washers 89 of the group disposed along the bolt8| are interposed respectively in the spaces between adjacent ones ofthe uppermost grids H with the bosses 90 thereof fitting snugly into thenext adjacent ones ofthe openings 2|, respectively, and extendingrespectively therethrough into the recesses 9| of the "next adjacentones of the washers 89. Similarly-the washers 89 of the group disposedalong the bolt 82 are interposed respectively in the spaces between theadjacent ones of the lowermost grids Additional washers 89 may be placedon the bolts 8| and 82 at opposite ends of the row of resistanceelements. The margin of metal around the opening2| of each of the gridsH is thus disposed between an annular surface around the boss of one ofthe washers 89 and an annular surface around the recess 9| of the nextadjacent one of the washers 89.

The respective groups of the washers 89. on the bolts 8| and 82 are heldin position by nuts 92 threaded on respective opposite end portions ofthe bolts. At the end portion of the bolt 8| nearest the end frame 69, asuitable lock washer 94 and a plain washer 95 are interposed between thenut 92 and the outermost one of the washers, 8.9- on the bolt 8| and, atthe end portion of the bolt 82 nearest theend frame 69, a lock washer 94and a plain washer 95 are alsointerposed between the nut. 92 and theoutermost one of the *washers 89 on the bolt 82. Similar lock washer-s94 and plain washers 95 are used respectively on the end portions of thebolts 8| and 82 nearest. the end. frame 69. At-the end nearest the endframe 68, however, the respective bosses 99 of the outermost ones of theinsulating washers 89 are received respectively in recesses 96 (Fig. 4)of insulating washers 91 received on the respective bolts 8| and 82 andhaving planular outer surfaces in engagement with the respective washers95.

An electric circuit through the resistor of Figs; 2, 3, and 4 can betraced'as follows:

Starting at the terminal member |2 at the front ofthe resistor and whichforms part of the resistance element loclosest to the end. frame 69, thecircuit is from the bracket portion 3| thereof through its tongueportion 28 and the spot welds 56 (Fig. *1) into the offset portion 24 ofthe uppermost grid ll of this first one of the resistance elements I 9and thence through this grid across the upper portion of the resistor.'Atlthe rear. of the resistor, the circuit continues from the uppermostgrid ll of the first of the resistance elements In downwardly throughthe spot welds 54 (Fig. 1) into the tongue portion'28 of the other orrear terminal member I2 of the first resistance element l0 and from thetongue portion 29 thereof through the spot welds 55 (Fig. 1) into thelowermost grid I I of the first resistance element It]. The circuit isthen through this lowermost grid back across the bottom portion of theresistor to its offset portion 24 which is spot welded to the tongueportion 49 of the front terminal member 5 of the first of the resistanceelements l4 nearest the end frame 69. From the tongue portion 4| of thisterminal member I5 the circult is through a pair of the spot welds 68(Fig. 1) into the offset portion 24 of the uppermost grid ll of thefirst of the resistance elements i4 and thence through this grid acrossthe top portion of the resistor. At the rear of the resistor, thecircuit continues downwardly througha pair of thespot welds 58 into theother or rear terminal member l5 of the first of the resistance elementsl4 and from. this member l5 through a pair of the spot welds 59 (Fig. 1)intothe lowermost of the grids H of the first of the resistance elementsM. The circuit then extends through this lowermost grid H across thebottom portion of the resistor towards the front and into its offsetportion 24 which is spot Welded to the tongue portion 29 of: the frontterminal member I22 of the next adjacent one. oftheresistance elements.-I0.

The circuit continues in likemanner back and for-th-v across the Iresistor until. the resistance element L L nearest the. end frame. 68;is reached.

It will be understood. that lead-in conductors may be secured to any of.the terminal members I21 and I5 atthe front: and. rear of the resistorto select increments of the total resistance of the resistor for use inan external electric circuit. Although in the resistor as shown. all oftheresistance elements I and I4 in the row are connected to form acontinuous series circuit from one end. of the resistor to the other, itwill be understood that groups of series-connected resistance elementsI0 and I4 may-be disposed along the supporting bolts 64 and 05andlelectrically isolated from each other.

In the modified resistor of Figs. 7 and 8, complementary compositeresistance elements I00 and I0,I, each comprising a pair of. individualgrids I02v similar to the grids II but not having ofi-set portions, arearranged alternately in a row along the main supporting bolts 64 and65-.and the bolts SI and 82 are used to support intermediate portions ofthe grids I02. Theinsulating washersllfiland 89 may beused asin theresistor of Figs 2, 3, and 4v to hold the elements I00 and, IOI infiat-wise spaced relation.

Each of the composite resistance elements I00 is assembled byoverlapping the outer end portion of an end leg I04 (Fig. 8) of one ofthe individual grids I02 on the tongue portion 28 of one of the terminalmembers I2. and securing it thereto asby a pair of spot welds I09, andby overlapping the outer end portion of the end leg I04, of another oneof the grids. I02 on the tongue portion 29 of. the same one of theterminal members I2. and securing it thereto as by a pair of spot weldsI05. When so welded to the tongue portions 28 and 29, the two grids I02lie in the same plane and extendifrom the terminal member I2 in the samedirection with their longitudinal axes parallel to each other.

Each of the resistance elements I00 also comprises aterminal member IIO(Fig. '7), similar to the terminal members I2, but having its tongueportions bent, in opposite directions from its body portion to definerespective angularly disposed portions IIIand II2, between its bodyportion and respective o ter end portions H4 and N5 of the tongues. Theend portions. [I4 and H5 are bent so that they lie in respective planeswhich are spaced from but parallel to the plane of the body portion.Each of the resistance elements I00 is completed by overlapping theofiset end portion II4 of one of the terminal members IID on an end legIIG opposite from the end leg I04 of the uppermost one of the grids I02thereof and securing it thereto as by a pair ofspot welds II8.

Each of the composite resistance'elements IOI is assembled byoverlapping the outer end portion ofthe end leg I04 (Fig. 8) clone ofthe grids I02 on the tongue portion 4| of one of the terminal members I5and securing itthereto as by apair of spot welds I I9; and.byoverlapping the outer end portionof the end leg I0 4' of another oneof the grids I02 on the tongue portion 400i the same one'of the terminalmembers I5 and securing it thereto as by a pair of spot Welds I Each oftheresistance elements: I 0I also comprises a terminal-member I2 (Fig.'7) similar to the terminal members I5; but havingitstongue portionsbentin opposite directions fromits bodyportion'. to define respectiveangularly disposed portions: I24 and I25 between its body port-iomandrespectivelouter endportions I20 and I29 of the tongues. The endsportions. I28: and I2t are bent so. that: they lie in respective planeswhich arespaced' frombut parallel to the: plane of the body portion.Each of the resistance elements MI iscompleted v by'overlappingtheoffset end portion- IzZfiof; onesof"theterminall members I-2 I on theendlegr I I001 the uppermost-one of -the grids: I02 thereof-andsecuring-it thereto as by a pair of: spot welds I30.

Ilhe resistance elements. I01 and I02 are asa sembled:alternatelydn arow on the bolts 64 and 05-110 forms a resistor with the bracketportions 3d: and 42; of the terminal members I2 and I5 respectively; at:therear of the resistor: extending: in-the same direction, on tothe=lef-tas viewed in- Fig; 8; andawith bracket portions I3 I and Iz32of theiterminal members LID-and I-M at thefront of: the; resistorextending in: thesamedirection orlto theleftas-viewed in- Fig. '7:

Except for the offset end portion I' IS'nearest' thealef t hand endof'the resistor (F-ig; 7 the-end portions lllfi otthe terminal membersH0 ex -l tend toward and engage the end leg: HIS of the lowermost grid I02- of' the-next adj acent resistance element: I0 I to whichtheyareelectricallyconneoted after the resistor is-.assembled=as by apair of= spot welds- I-3'4l Likewise, the-offset endportions; I29 Oftheterm-inal members I-2I extendj toward and engage the end leg-I IQ of thelowermost grid; I02" of; the next adjacent: resistance element I00"towhich; they are electrically connectedafter the'resistor isassembledasbya pair; of spotwelds I35; Thus an electric circuit throughthe resistor of'Figs. 7-and'8*is compl ete d through spot welded jointsas the resistor of, Figs; 2; 3, and t and the ofiset'. tongue portion jle. t rmina memb s, I I t nd I 2| p ovi e. th dvan e sp fiheo s t portins .4, I

Ha insfihis d sc ibed my. invention. laim.

ele tric e isto o pris n a. g o p. i eenel'allv la anmeta lic id emh saranse pairssw hs e in iv dual l gr s l lfn ach pair in generally,deewisesnacedl ande n rallypaialie relation, andithe sev al; pai s ar aned; n l k pa ed; nd eenera y arallel elation; o. a h heinvhereby adjacnt on sh pairs s? l ett s era lyl One from. the Other,- I each f; thegrid members of each having, at one n l he. ir afi stnt e a ueortlonlele trical y ond cti e i id upp rt nem mbers 're t ve o the. a tnd. h .elec r cally terronnectin dr ma n m onded to. he-firsts g. t 0ni. s scr mma e. and hereby hol in 7 he. id 0 members) f s. ssociatedpair fix l n said. enerally deewi e paced" and: r-ll l fi-ner ll l e tinr ach er dsmember o ac pair; hav n I a ficchdilltesml ,lug po tion. atts pposite; ect. dditio al l tri al y conduc: i e igid upportin mem ersion the ha sp apastic 1y, ach additional supporting m mber i e lectically-1 onne te and.- permanently bonded at oner portion .to ,thesecOBdlug portion ne. el'i member ts. ass c ated par. atanothgzrportion,tovthelsecond.lug portion or gridme nb i anext .adiacentpair andmeanscooperating withisaid suppo ting; members and said .4 additionalsupporting, members (for holding aid eirsl n id. flatwis spa d andtenerally para lel elatlonl.

Theesist nof. lalln.rll h racterized; inthat each of said first lugportions is substantially coplanar with the major portion of itsassociated grid member.

3. The resistor of claim 1 characterized in that each of said gridmembers comprises a row of spaced bar portions and integral connectingportions at the ends of adjacent bar portions and forming therewith asinuous electrical path extending endwise of the row, and said lugportions are the respective end ones of said bar portions.

4. The resistor of claim 1 characterized in that all of the grid membersare substantially identical.

5. The resistor of claim 1 characterized in that eachof the two gridmembers connected together by an additional supporting member are alsooffset edgewise from each other.

6. The resistor of claim 1 characterized in that each of said second lugportions is oiTset laterally from the plane of the major portion of itsassociated grid member.

7. The resistor of claim 1 characterized in that said second lugportions of each pair of grid members are offset laterally from, and inopposite directions respectively from, the plane of their associatedpair.

8. The resistor of claim 1 characterized in that each additionalsupporting member has a planar portion and the connected portions ofeach of said additional supporting members are offset laterally of theplanes of the pairs in opposite directions, respectively, .from itsplanar portion.

9. The resistor of claim 1 characterized in that said supporting membersand additional supporting members have mounting holes, respectively, andsaid last mentioned means comprises a pair of bolts passing through themounting holes in said supporting members and in said additionalsupporting members, respectively.

10. The resistor of claim 1 characterized in that at least some of saidsupporting members, and at least some of said additional supportingmembers, have extending portions, respectively, and each of saidextending portions is arranged for connection with a Wire.

11. The resistor of claim characterized in that the extending portionsof adjacent ones of the supporting members extend laterally of theplanes of the members, each in the same direction from its associatedmember at least close to the plane of the next adjacent member, and saidextending portions on said adjacent ones of said supporting members arespaced from each other in the general direction of the edgewise spacingof the grids of each pair.

12. An electric resistor comprising a plurality of generally planarU-shaped metallic resistance elements each having a rigid base portionand a pair of arm portions extending therefrom and fixedly held ingenerally endwise spaced relation to each other thereby, each of saidelements having a first mounting means at its base portion and a secondmounting means electrically connected to, and permanently bonded to, thefree end portion of one of said arm portions, said second mounting meansbeing ofiset from the plane of the remainder of said element and lyingin a plane spaced from and generally parallel to the plane of saidelement, and supporting means for said resistance elements cooperatingwith said first and second mounting means, respectively, of eachelement, and thereby supporting said elements in substantially paralleland flatwise 14 spaced relationship with respect to each other with eachof said second mounting means extending toward, and being in electriccontact with, and permanently bonded to, the free end portion of an armportion of an adjacent element.

13. The resistor of claim 12 characterized in that one of said armportions comprises a metal strip forming a circuitous current pathincluding a succession of parallel legged loops alternately extending inopposite directions from the longitudinal axis of their associated armportion and including an elongated portion at the free end of the stripand extending toward but not intersecting the longitudinal axis of theresistance element as a whole, and said second mounting means areelectrically connected to, and permanently bonded to, said stripportions, respectively.

14. The resistor of claim 12 characterized in that each of said armportions of each element is a separate strip of electric resistancematerial and each base portion of each element is a separate electricconductive member electrically connected to, and permanently bonded to,the strips of the element of which it forms a part, and, constitutessaid first mounting means.

15. The resistor of claim 14 characterized in that each of saidconductive members is spot welded to the strip of the element of whichit forms a part.

16. The resistor of claim 12 characterized in that both of said free endportions of each of the U-shaped resistance elements are offset inopposite directions, respectively, from the plane of the remainder oftheir associated element.

17. An electric resistance element adapted to be assembled in aresistance unit which includes a plurality of said resistance elementsarranged in fiatwise and generally parallel spaced relationship, saidelement comprising a pair of metal supporting members permanently bondedto, and supported in fixed position by, and electrically connected by, agenerally planar intermediate metallic resistive portion, one of saidsupporting members lying substantially in the plane of said resistiveportion and the other of said supporting members being ofiset from thegeneral plane of said resistive portion and lying in a plane which isgenerally parallel to the general plane of said resistive portion, asecond substantially planar resistive portion permanently bonded to, andsupported in fixed position by, and electrically connected to, said oneof said supporting members and disposed in edgewise spaced and generallyparallel relation to said first resistive portion and generally coplanartherewith.

ALVIN C. DYER.

References Cited in the file of this patent UNITED LTATES PATENTS NumberName Date 1,501,638 Weimer et a1. July 15, 1924 1,525,460 Miller Feb.10, 1925 2,378,056 Wright June 12, 1945 FOREIGN PATENTS Number CountryDate 361,986 Great Britain Dec. 3, 1931 OTHER REFERENCES Kutcher et al.,The Welding Journal, Oct. 1948, Des. 827-830.

